Connecting device for interconnection of optical fibres

ABSTRACT

Connection device for connecting the end portions of optical fibres (30) comprising insertion means (12) and receiving means (11) designed for cooperation with at least a centering means (37) for radial and axial centering of the end portions of the optical fibres relative to each other. The centering means (37) is comprised of a sleeve (38) being closed in cross-section and provided with internal guiding elements (39) in the form of centering shanks extending in the longitudinal direction, and external guiding elements (40) in the form of ridge formed portions (40) extending in the longitudinal direction of the sleeve connected to the centering shanks and designed to allow the centering shanks to radially spring in a direction toward and from the center axis of the sleeve.

The present invention refers to a connection device for connecting theend portions of axially opposite to each other situated optical fibresand comprising insertion and receiving means designed for cooperationwith at least a centering means for radial and axial centering of theend portions of the optical fibres relatively each other.

BACKGROUND OF THE INVENTION

In the last few years connection devices have been developed to connectoptical fibres with each other, so that the fiber ends are situatedexactly axially opposite to each other. An example on such a connectiondevice is shown in the swedish patent 426 882. A difficulty withconnection of optical fibres at the ends to each other is their smalldiameter, which amounts to one or a few tenths of a millimeter, whilethe optical core thereof can have a diameter of 10-50 um. Aneccentricity of the end portions of the fibre cables of one or a fewthousand parts of a millimeter thus constitutes a rough deviation,whereby the losses increase drastically. Very high demands are thus puton the tolerances of the connection device, which leads to complicatedconstructions and high manufacturing costs.

Connection devices are previously known (IBM Technical DisclosureBulletin, volume 21 on Oct. 5, 1978) for connection of optical fibres,where the fibre is guided and fixed by three axial rods arranged in aconical guiding body, which is radially slotted. The guiding body isinsertable in a receiving means with corresponding conicity, whereby theguiding body by means of a cap nut can be pressed into the receivingmeans. Since the conical part of the guiding body in its rear partpasses over into a solid annular shaped member, a bringing together ofthe guiding body in the receiving means only the front part of theconical part will be compressed, which means that the fibre only isguided and fixed in its front end. If the tightening pressure isincreased to get a larger part of the fibre fixed inside the guidingbody the pressure stress at the extreme ends of the guiding body willbecome so large that the fibre will be crushed.

Through DE-B2-27 57 215 is known a connection device where a number ofrods are surrounded by a slotted circlip, the function of which is tokeep the rods together and thereby form a receiving means, in which fromboth ends is insertable a connection pin. If the fibre diameter in oneof the connection pins is larger or smaller than the fibre diameter inthe other connection pin, only one of the connection pins will be fixedin the receiving means, while the other will take an eccentric positionrelatively the first connection pin.

OBJECT OF THE INVENTION AND MOST ESSENTIAL FEATURES

The object of the present invention is to accomplish a connection devicefor optical fibres of the above mentioned type, with which is provided:

a) a reliable and very exact centering of the fibre end portions withvery simple means;

b) a possibility to connect optical fibres of different thickness withthe end portions situated opposite to each other in exact coaxialpositions;

c) a security that the optical fibre will not be deformed at theconnection with the connection device;

d) a connection of the optical fibre with the insertion means and thiswith the receiving means without using special tools and glued joints orcasted joints.

This task has been solved by the centering means being constituted by asleeve being closed in cross section provided with internal guidingelements in the form of centering shanks extending in the longitudinaldirection and external guiding elements in the form of ridge formedportions likewise extending in the longitudinal direction of the sleeveconnected to the centering shanks and designed to allow the centeringshanks to radially resiliate in a direction towards and from the centreaxis of the sleeve.

DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail in some embodimentswith reference to accompanying drawings.

FIG. 1 shows a section through an insertion means contained in aconnection device according to the invention.

FIG. 2 is a section along the line II--II in FIG. 1.

FIG. 3 is a section along the line III--III in FIG. 1.

FIGS. 4, 5, and 6 show in perspective three alternative embodiments ofcentering means.

FIG. 7 shows a section through a receiving means contained in theconnection device according to the invention.

FIG. 8 shows a section of a connection device assembled from aninsertion device and a receiving device.

FIG. 9 shows a section along the line IX--IX in FIG. 8.

FIG. 10 shows a section through a receiving means with integratedcentering means.

FIG. 11 is a section along the line XI--XI in FIG. 10.

FIG. 12 shows a section through a modified connection device accordingto the invention.

FIG. 13 shows a view from above of a centering means contained in theconnection device according to FIG. 12.

FIG. 14 is a section along the line XIV--XIV in FIG. 13.

DESCRIPTION OF EMBODIMENTS

A connection device according to the invention for connection of the endportions of two optical fibres may consist of a receiving means 11 andtwo insertion means 12, of which the last mentioned are axially arrangedone optical fibre each and which insertion means are connectable withthe receiving means 11.

The insertion means 12--shown in FIG. 1--comprises a plug 13, which inits front end portion 14 is provided with an axial channel 15, which insection is Y-formed. The channel 15 passes over to a concentric withrelation to this provided central through bore, which consists of afirst section 16 with a small diameter, a second section with a somewhatlarger diameter and a section 19 with considerably larger diametersituated in the rear end portion 18 of the insertion means.

The channel 15 which is Y-formed in section, passes over in radial slots20, situated in the extensions of the Y-formed channel members. Thebottom 21 of the slots 20 is conical, that is slants like a ramp fromthe channel members and upwards, with its largest depth closest to thechannel 15. At the bottom 21 is provided a hook-shaped recess 22. Theplug 13 is further formed with a shoulder 23, which forms a stop facefor a cap nut 24.

As can be seen from FIG. 8 the bore is intended to receive an opticalfibre cable 25 the stress-relieving membrane 26 of which has beenexposed and turned over the cable, which is clamped by means of aclamping sleeve 27. In the middle bore 17 is placed the secondaryprotection 28 which is released from the cable cover and up to thesmallest bore 16 the primary protection 29 extends. The totally exposedoptical fibre 30 has been thread through the bore 16, which fibre iscentered and fixed by the connecting pin 32 of the insertion means,which connecting pin in the shown embodiment consists of threecylindrical rods 33 with circular cross section, placed into contactwith each other, so that these between each other form a central slot orchannel 34 for receiving the optical fibre 30. About a third of the rodsare situated outside the plug 13, the middle third is situated in theY-formed channel 15, while the rear third of the rods is shaped with asmoothed down portion 35, which is intended during the mounting to slidealong the conical bottom 21 of the slots 20. In the smoothed downportion 35 is also provided a lip 36, which cooperates with thehook-formed recess 22 at the bottom 21 of the slot 20. The conicity ofthe bottom of the slot is chosen such, that the rods 32 at theirinsertion in the plug through the Y-formed channel 15, will springoutwards and act like cantilevers, where the rear end of the rodsprovided with the smoothed down portion 35 forms one of the cantileversand the cylindrical part of the rods the other cantilever. The conicalbottom 21 of the slots 20 thus on the part of the rods between which theoptical fibre 30 is placed exerts a radial inwards directed forcetowards each other, which effectively guides and fixes the optical fibrebetween the rods. The part of the fibre 30 projecting outside the rodsis cut off and the surface of the section is polished.

The mounting of the fibre cable in the insertion means 12 is carried outby peeling off the primary and secondary protection from the cable. Whenthe optical fibre 30 has been exposed, it is thread through the bore 16and is placed in the slot or channel 34 which is formed between the rods33. The fibre 30 is fixed in the channel 34 by the smoothed down portion35 with the lip 36 of the rod 22 being snapped in behind the lips 22.The cover of the cable is clamped in the bore 19 by means of theclamping sleeve 27. Thereby has been achieved a simple insertion means,the optical fibres of which are exactly, centrally and coaxiallyoriented relatively the rods 33. The object is now to center two suchinsertion means relatively each other in such a way, that the connectionpins come into exact positions relatively each other and where thetolerances are so small that the accuracy stated by way of introductionis fulfilled. This task has been solved by means of a centering means37, consisting of a sleeve 38, which is provided with internal guidingelements 30 in the form of radially resilient centering shanks, wherebythe resiliency of these shanks is accomplished by means with theseconnected external guiding elements 40 eg. in the form of axial edgefoldings, ridges or the like of which the bent edge 41 forms theexternal contact surface of the centering means, such as is shown inFIG. 9. The free space between the centering shanks 39 is somewhat lessthan the external limitation of the connection pin 32, so that when thisis inserted in said sleeve 38, the centering shanks are pressed slightlyradially apart. In order to restrict this expansion only to the portionof the sleeve where the connection pin is inserted, the sleeve 37 may beprovided with circumferential slots 42 (FIGS. 4 and 5).

The sleeve can be given various forms and be adapted to connecting pinsof different form and dimension and also to the number rods 33 containedin the connection pin 32, as is shown in FIGS. 4, 5 and 6.

The receiving means 11 shown in FIGS. 7-9 is on the outside providedwith threads 52 fitting to the threads 53 on the sleeve nut 24 of theinsertion means 12. Thus two insertion means 12 which are insertableinto the ends of the receiving means thus by means of the sleeve nuts 24may be fixed to the receiving means, whereby the guiding of the frontend portion 44 of the insertion means is carried out by cooperationbetween this and a corresponding recess 45 in the front respectively therear end of the receiving means 11. The receiving means contains twomembers and each member at one end is provided with a flange 54 whichflanges in the assemblied state of the receiving means are situatedopposite each other. At the end of each member provided with a flange 54is provided a central recess 55 coaxially arranged with the recesses 45and a bore 56 interconnecting these recesses. In the recess 55 is placedthe centering means 37, whereby the inner diameter of the cylindricrecess 55 corresponds to the outer diameter of the centering means. Thelength of the recess 55 mainly corresponds to the length 37 of thecentering means, so that this is fixed to its position.

The embodiment according to FIG. 10 and 11 differs from the embodimentsdescribed above by the receiving means 11 and the centering means 37being produced in one piece in a resilient material, e.g. throughextrusion. The external guiding elements of the sleeve 38 are firmlyconnected with in section circular internal cylindric envelope surfaceof the receiving means. The sleeve 38 consists of three or another oddnumber of centering shanks 39, which are connected to said envelopesurface by radial flanges 43.

A further variant of the connection device according to the invention isshown in the FIGS. 12-14. The centering means 37 in this embodiment isconstituted by a conical sleeve 47, formed with resilient sectors 48,consisting of material weakened axial portions 49. In this example theinternal wall surface of the sleeve constitutes the inner guidingelement 39 of the centering means 37, while the outer guiding element 40is constituted by those parts of the outer envelope surface, which aresituated between the resilient sectors. The receiving means 11 isprovided with conical seats 50 corresponding to the conicity of thecentering means 37. The conical sleeve 47 on the inside is formed afterthe external form of the connection pin 32, which in the embodimentshown in FIG. 12 has cylindric form. The connection pin 32 of theinsertion means 12 is provided with a circumferential flange 51, whichforms a shoulder against one of the end surfaces of the conical sleeve47. By means of a sleeve nut 24 the sleeve 47 is pressed into theconical seats 50 of the receiving means, whereby the sleeve along itstotal length forms around the connection pin 32 of the insertion meansand centers this to the center of the sleeve. When the sleeve is pushedinto the conical seat the thin portions 49 bulge outwards, which isshown with dash dotted lines in FIG. 13, and the internal limitationthus can adapt to the diameter of the insertion means. The tolerance ofthe insertion means is normally not more than 2-3 μm, why a relativelysmall deformation of the sleeve occurs. The length of the insertionmeans is ground in relation to the cone of the sleeve with an accuracyof e.g. 3 μm. At certain tightening moment of the sleeve nut 24, thefiber end will come into an axially accurate position, as is evidentfrom FIG. 12 there is a possibility in this way to center insertionmeans with different diameters. The centering means is adapted to thedifferent diameters, but the same receiving means can be used. Thismeans that in the market available different systems with differentdiameters of insertion means may be connected.

TABLE OF REFERENCE DESIGNATIONS

11 receiving means

12 insertion means

13 plug

14 plug front end portion

15 Y-formed channel

16 central bore with small diameter

17 central bore with larger diameter

18 plug rear end portion

19 bore with substantially larger diameter

20 radial slot

21 the conical bottom of the slot

22 radially projecting means e.g. a lip

23 shoulder

24 cap nut

25 fibre cable

26 stress-relieving membrane

27 clamping sleeve

28 secondary protection

29 primary protection

30 optical fibre

31

32 connection pin

33 rods

34 channel

35 smoothed down portion

36 lip

37 centering means

38 sleeve

39 inner guiding elements, e.g. centering shanks

40 outer guiding elements, e.g. azial edge foldings

41 bent edge

42 slots

43 radial flanges

44 front end portion

45 corresponding recess

46 bow formed portion

47 conical sleeve

48 resilient sectors

49 material weakened portion

50 conical seats

51 circumferential flange

52 external threads at the receiving means 11

53 internal threads at the sleeve nut 24

54 flange

I claim:
 1. Connection device for connecting the end portions of axiallyopposite to each othe situated optical fibres (30) and comprisinginsertion (12) and receiving means (11) designed for cooperation with atleast a centering means (37), in form of a conical sleeve (47) providedwith guiding elements (39) extending in the longitudinal direction ofthe sleeve cooperating with conical seats (50) of the receiving means(11) for radial and axial centering of the end portions of the opticalfibres relatively each other, characterized therein, that the insertionmeans (12) comprises at least three cylindrical rods (33), which betweenthemselves form a central channel (34) for receiving of the opticalfibres (30), and which rods with their internal end portion are fixed inthe retainer (13) of the insertion means (12) and with their externalend portion are situated outside this forming its connection pin (32),designed for cooperation with the centering means (37), and that theattachment end is provided to be bent radially outward and fixed inthese positions during simultaneous compression of the rods in adirection towards the center axis of the insertion means (12), and thatthe conical sleeve (47) is closed in cross section by the resilientsectors (48) which consist of material weakened axial portions (49)along the entire length of the sleeve, which sectors are elasticallydeformable and/or in section curved, folded or in an other wayelastically compliant.
 2. Connection device according to patent claim 1,characterized therein, that the attachment end of the rods (33) isformed with at least one radially projecting means (36) for cooperationwith corresponding means (22) at the insertion means (12) for axiallocking of the rods (33).
 3. Connection device according to patent claim1, characterized therein,that the rods are formed as cantilevers, onearm of which is constituted by the attachment end of rod, which isprovided with a smoothed down portion (35), which is arranged tocooperate with a conical guiding surface (21) in the insertion means(12), and that the guiding surfaces (12) are designed to press saidattachment ends radially outwards, so that the external end portionsformed by the connection pins of the insertion means are pressedradially into contact with each other.
 4. Connection device according topatent claim 1, characterized thereinthat the resilient sectors of thecentering means (37) are constituted by axial edge foldings (40), ridgesor the like, that each edge folding (40) contains resilient centeringshanks the bent edge (41) of which is formed to constitute one of theexternal guiding surfaces of the centering means, and that the portionsbetween the edge foldings are formed to constitute the internal guidingand centering surfaces (39) of the centering means (37).
 5. Connectiondevice according to patent claim 1, characterized therein,that thecentering means (37) is constituted by a conical sleeve (47), theresilient sectors (48) of which consist of material weakened axialportions (49), which are elastically deformable and/or in sectioncurved, folded or in an other way elastically compliant.
 6. Connectiondevice according to patent claim 1, characterized therein,that thecentering means (37) is constituted by a sleeve (38) on the insideprovided with axially oriented centering surfaces (39) corresponding tothe number of rods (33), which surfaces each shom a bow formed portion(46) connected to the inside of the sleeve by means of radial flanges(43).
 7. Connection device according to patent claim 5, characterizedtherein,that the receiving means (11) is formed with double sidedreceiving points for two coaxially connectable insertion means (12) fromeach side, and, that each receiving point is shaped with a conicitycorresponding to the conicity of the centering sleeve (37).
 8. A devicefor connecting the end portions of optical fibres (30)comprising:insertion means (12) for receiving the end of an opticalfibre, tubular receiving means (11) having a central opening extendingtherethrough, said opening having conical seats (50) at each endthereof, said conical seats being in axial alignment with each other andopening outward from said receiving means (11), a conical sleeve (37)having an inner passage extending therethrough and an outer conicalsurface dimensioned to conform to and to mate with said conical seats(50), said sleeve (37), including a plurality of resilient, flexiblesectors (48) which extend longitudinally along the entire length of saidsleeve (37), said sectors (48) being elastically deformable and/or insection curved, folded or otherwise elastically compliant, and saidinner passage dimensioned to receive said insertion means, and means forsecuring (24) said conical sleeve (37) within said opening in saidreceiving means (11) wherein said outer conical surface of said conicalsurface of said conical sleeve (37) is forced into engagement with saidconical seat (50).